Molecules of some compounds can be excited from a ground state to an excited state using a beam of light. During this excitation, individual molecules absorb photons and shortly thereafter emit light having a longer wavelength than the beam of light. This emission of light after absorbing a photon is referred to as fluorescence.
Fluorescent spectroscopy is an inspection technique that involves the analyzing the spectral distribution of light emitted by a sample due to fluorescence. In an example approach, a light source illuminates a sample, causing some of the molecules within the sample to fluoresce. A detector then measures characteristics of the fluorescence, such as the intensity and/or wavelength of the light emitted by the sample.
An emission spectrum of a sample can be generated by exciting a sample at a particular wavelength and measuring the relative intensity of fluorescence over a range of detection wavelengths. Additionally or alternatively, an excitation spectrum of a sample can be generated by measuring the relative intensity of fluorescence at a particular wavelength while the sample is excited over a range of excitation wavelengths.